1. Technical Field
The present invention relates in general to a method of hollow core die-casting or thixoforming computer components and in particular to an actuator component for a computer hard drive having improved damping. Still more particularly, the present invention relates to computer hard drive actuator arms and E-blocks having a unitary body and a hollow core that can be filled with substances to improve the damping performance of the actuator arm or E-block.
2. Description of the Related Art
Computer hard drives that utilize a read/write head mounted on an air-bearing slider require optimal performance in order to achieve fast and accurate data retrieval and recording. In such systems, the slider is typically mounted onto an actuator arm or series of actuator arms, called an E-block. The actuator arm(s) holds the slider over the magnetic data storage medium, typically a moving disk. Due to the minute and rapid movement required of the slider to read and write data, the design and manufacture of the actuator arm is particularly critical.
In a computer hard drive, or magnetic disk drive, one or more magnetic disks are mounted on a spindle which rotates the disk(s) typically between 3000 and 15,000 revolutions per minute while the slider "flies" over the disks on the air-bearing generated by the compression of the air passing underneath the slider. The actuator arm on which the slider is mounted is a rigid support that moves the slider in order to locate the magnetic read/write head over the appropriate place on the disk.
The most common type of actuator arm is actually a series of arms stacked at a specified distance from one another called an E-block. Ideally, the E-block actuator arms should be stiff, and the inertia of its lateral movement across the disk minimized. This makes data access or reading time faster with smaller power requirements. A stiffer system will respond faster, as greater stiffness minimizes the time it takes the arm to "settle" or cease vibration. To reduce the settling time, the arm(s) should be have a large damping capability.
Properties of an actuator arm most important to the present invention relate to the actuator arm's structural response to an input disturbance. The response is head off-track amplitude (gain) and the input disturbance is a swept sine frequency to the voice coil motor ("VCM") used to drive the actuator arm in an arc across a moving disk. The response is a transfer function which is the output divided by the input for each frequency. There are four main actuator mode shapes that drive the off-track response. In ascending order of frequency they are: (1) butterfly mode, (2) S-mode, (3) M-mode, and (4) end arm mode. In general, it is desirable to have separation of frequencies of each arm so that the gains do not superimpose additively, thus low gain is best. Further, higher frequencies are good, especially if the frequency is greater than that of the sample rate or Nyquist frequency. Damping of a mode will absorb energy at that frequency, thus lowering gain and improving the disk drive performance.
Damping can be improved in actuator arms through adjustment of the material density of the arm, flexural modulus, and specific flexural modulus. A low material density is desired because a low density allows more material to be used to improve the stiffness of the E-block, while maintaining low mass and thus low inertia. A low material density can reduce cost by eliminating the need for incorporating weight reducing holes into the product. Including weight reducing holes in an E-block requires additional manufacturing steps which adds additional costs. Further, the holes may induce air turbulence which affects the performance of the head assemblies as they "fly" over the surface of the disk. Although Schirle et al. (U.S. Pat. No. 5,801,905) use this technique, subsequently filling the cutouts with lightweight plastic, this further processing adds even more to the cost of manufacturing the arm. Further, it may be difficult to ensure that the cutouts are filled such that the actuator arm surfaces are smooth and thus, do not cause air turbulence.
In light of the advantages to increasing the damping ability of the actuator arm, devices and modifications to the actuator arm have been proposed in the prior art that reduce the weight of the arms while attempting to increase the stiffness of the arms. Misso et al. (U.S. Pat. No. 5,627,701) disclose an E-block design in which each actuator arm is composed of a damping foam core with a non-porous stressed skin formed around the core. Ruiz et al. (U.S. Pat. No. 5,771,135) disclose a three part sandwich-design actuator arm that sandwiches the damping material between two suspensions. Although relatively lightweight, the manufacture of such a systems is complex, hence, the cost of manufacture is relatively large. Disk drives and their components are considered commodity products. Hence, the cost of the drive and the associated parts is a critical parameter in achieving sales of the product. Thus, there is strong incentive in the industry to find less costly ways of manufacturing actuator components.
One of the simplest and least expensive means of making actuator arms is through die-casting. This is because the major portion of the arm can be made as a unitary body at one time. However, there is a desire to further improve on the die-casting method of making actuator components by making the arms lighter and stronger. A proposed means of making the arms lighter while still maintaining the unitary body of having a die-cast body is by forming a hollow core in the arm that can then be filled with a substance. Die-casting that produces a hollow core suitable for actuator arms has not been achieved. Although Carden (U.S. Pat. No. 5,803,151) disclosed a method of making a hollow cavity in a structure, the process is limited to molten casting material. Further, it is not clear that this method would be suitable for actuator arms.
What is needed is an economical means by which damping can be improved in actuator components and other devices through hollow core die-casting, thixoforming, or other fluid material forming. The means of manufacturing the actuator component should take into account the desire for decreased weight and increased damping ability of the arm, as well as cost. Further, the E-block, actuator arm or other actuator component should be thermally stable to reduce distortion due to changes in the temperature due to use and/or the environment. The present invention is directed towards such a need.